netdev - [PATCH 1/6] bpf: Allow ctx access for pointers to scalar

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Date:   Tue, 21 Jan 2020 13:05:07 +0100
From:   Jiri Olsa <jolsa@...nel.org>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Cc:     John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Andrii Nakryiko <andriin@...com>,
        Yonghong Song <yhs@...com>, Martin KaFai Lau <kafai@...com>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        David Miller <davem@...hat.com>,
        Björn Töpel <bjorn.topel@...el.com>
Subject: [PATCH 1/6] bpf: Allow ctx access for pointers to scalar

When accessing the context we allow access to arguments with
scalar type and pointer to struct. But we omit pointer to scalar
type, which is the case for many functions and same case as
when accessing scalar.

Adding the check if the pointer is to scalar type and allow it.

Acked-by: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Jiri Olsa <jolsa@...nel.org>
---
 kernel/bpf/btf.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 832b5d7fd892..207ae554e0ce 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -3668,7 +3668,7 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		    const struct bpf_prog *prog,
 		    struct bpf_insn_access_aux *info)
 {
-	const struct btf_type *t = prog->aux->attach_func_proto;
+	const struct btf_type *tp, *t = prog->aux->attach_func_proto;
 	struct bpf_prog *tgt_prog = prog->aux->linked_prog;
 	struct btf *btf = bpf_prog_get_target_btf(prog);
 	const char *tname = prog->aux->attach_func_name;
@@ -3730,6 +3730,17 @@ bool btf_ctx_access(int off, int size, enum bpf_access_type type,
 		 */
 		return true;
 
+	tp = btf_type_by_id(btf, t->type);
+	/* skip modifiers */
+	while (btf_type_is_modifier(tp))
+		tp = btf_type_by_id(btf, tp->type);
+
+	if (btf_type_is_int(tp) || btf_type_is_enum(tp))
+		/* This is a pointer scalar.
+		 * It is the same as scalar from the verifier safety pov.
+		 */
+		return true;
+
 	/* this is a pointer to another type */
 	info->reg_type = PTR_TO_BTF_ID;
 
-- 
2.24.1